The proposed study is designed to investigate the concept of functional and structural asymmetry in the photosynthetic membranes found in bacteria belonging to the family Chromatiaceae and the family Chlorobiaceae. In terms of the cytology of intracytoplasmic membranes, these bacteria comprise a variety of ultrastructural types. Our efforts have been directed towards examining the relationships between the different types of photosynthetic intracytoplasmic membranes and the accumulation of sulfur in the cells in the form of "membrane-bound" sulfur granules. From our cytological data, we have developed a hypothetical scheme on the development of chromatophores and sulfur granules in Chromatium. This scheme proposes that the "membrane" surrounding the sulfur granule is derived from the chromatophore membrane. Using isotopic tracers and a variety of biochemical and enzyme-localization experiments, we plan to test this pypothesis and determine the vectorial arrangements of proteins on the plasma membrane, chromatophore membrane, and the "membrane" surrounding the sulfur granule.